Alpha Technologies Cordex Controller Ver.3.1x - Manual (Page 116)

0700015-J0 Rev B 114
10.1.3 Typical UDP Transport
• Agent listens on UDP port 161.
• Responses are sent back to the originating NMS port from a dynamic port, although many agents
use port 161 also for this target.
• Maximum SNMP message size is limited by maximum UDP message size; i.e. 65507 octets.
• All SNMP implementations have to receive packets at least 484 octets in length.
• Some SNMP implementation will (incorrectly or not) handle packets exceeding 484 octets.
• Asynchronous Traps are received on port 162 of the NMS.
• UDP is more suitable than TCP when dynamic route changes occur often; e.g., when there are prob-
lems in the network.
• UDP packets minimize the demands placed on the network (no resource tied up as with connection
mode).
• Agent and NMS are responsible for determining error recovery.
SNMP is transport independent (although the original design was connectionless transport function,
which corresponds to the UDP protocol) and can be implemented on other transports as well:
• TCP (Connected approach)
• Direct mapping onto Ethernet MAC level
• Encapsulation onto X25 protocol
• Encapsulation onto an ATM Cell
Figure 141 — UDP transport (trap event)